Associative path

The k2 term suggests a simple bimolecular process in which nucleophilic attack by Y leads to a SN2 reaction. Associative paths will involve a 5-coordinate (sp or tbp) intermediate, and the relative rarity of isolable 5-coordinate plati-num(II) species - compared with 4-coordinate - is not inconsistent with their involvement as reactive intermediates (Figure 3.81). 

Fig. 14. Reaction energy diagram for the formation of DME from methanol, proceeding by an associative path without intermediate methoxy formation. Energies are in kj/mol ads refers to an adsorbed complex, ts to a transition state. Reprinted with permission from Ref. 244. Copyright 1996 American Chemical Society.

Another intriguing aspect of Mr. A s dream is that it seems to be divided into two fairly distinct portions. In the first portion, the A-A parallelism occurs when Mr. A leaves the elevator, the A-B parallelism begins. Why did this shift occur One possibility is that the events happened in the order presented in the dream. That is, Mr. A acquired information about Mrs. A s dream by psi and/or influenced her dream by talking in his sleep and/or arrived at a similar dream via parallel associative paths he then acquired the information about Miss B s activities and dream by some form of psi. One could imagine Mr. A warming up his psi abilities on his wife and then reaching out all the way to Miss B. 

It is, of course, possible to set up rate expressions for the formation of X. B by the upper (diffusion-controlled) and the lower (pre-association) paths in Scheme 3, but for our present purpose it is sufficient to consider only the three... 

Interaction within encounter pairs. The above arguments have assumed that there is no interaction between the components in the encounter pairs A. B and B.X (Scheme 3) but this is probably unrealistic. Stabilization of the encounter pair A. B by charge-transfer interaction should favour the pre-association path by reducing the value of k 3 and possibly also increasing that of k4 [cf. equation (46)].22 Thus, in the nitration of neutral amine molecules (X) by nitronium ions (B) in concentrated sulphuric acid, interaction between the components in the encounter pair ArNHJ.NOJ should increase the acidity of the N—H hydrogens and facilitate the formation of the free amine. In the bromination of aromatic compounds (B) by HOBr(A), interaction between the components should increase the concentration of the encounter pair ArH. HOBr and facilitate the protonation of the hypobromous acid. 

One computational study see Molecular Orbital Theory) has appeared using RhCl(PH3)2 to model the rhodium-catalyzed hydroboration of ethylene see Hydroboration Catalysis). Both associative and dissociative pathways were examined (equation 47). In the associative path, three possible... 

This can be applied for the scrap process described above. We choose again Gaussian pulses, but with parameters such that the path is now close to the optimal one—that is, a level line. The numerical calculation is shown in Fig. 5, and the associated path (b)opt is shown in Fig. 4. We can see that for smaller pulse areas compared to the ones used in Fig. 3, we obtain a better population transfer, which, moreover, is monotonic. 

Associative path (c) has been mainly observed for nickel(II) complexes [BOSS], This is because nickel(II) has a higher propensity to make five-coordinate species than palladium(II) and platinum(II). A steric condition is another important factor. Thus the reductive elimination from bipyridine-coordinated dialkyl-nickel complexes is known to be effectively accelerated by addition of n-acceptor olefins such as maleic anhydride and acrylonitrile to the systems (Scheme 9.8)... 

As association nears completion, all the intermediate species concentrations diminish, but so does the rate of association, which behaves rather like a second order reaction in the excess intermediates. In a fuel-rich system reactions (c) and (—c) remain first order in excess intermediates, and thus this equilibrium condition becomes progressively better established, while reactions (a), (b) and (d) retain the same tendency to be perturbed by reactions (e) and (g). In fuel-lean mixtures, only reaction (d) improves its equilibration capability, as the competitive relationship between the primary association path, reaction (/), and reaction (a) is influenced only by [M]. 

Figures. . Wilkinson mechanism for rhodium-catalyzed hydroformylation (a) associative path (b) dissociative path. R = i CH2CH2- or i CH(CH3)-.

One group transforms are similar but are keyed by one specific group with an associated path (not as... 

---